1. Field of the Invention
The present invention relates to an internal combustion engine control apparatus and more particularly to an internal combustion engine control apparatus for accurately calculating a cylinder intake air amount and a cylinder intake exhaust gas recirculation amount.
2. Description of the Related Art
In order to appropriately control an internal combustion engine (although also referred to as an engine, referred to as an internal combustion engine in the following explanation), it is important to accurately calculate the amount of air taken into a cylinder and to perform fuel control and ignition timing control in accordance with the amount of air taken into the cylinder flow. With regard to fuel control, when feedback control can be performed in such a way that, primarily, a fuel, the amount of which causes a desired air-fuel ratio for a cylinder intake air amount, is injected, almost excellent controllability can be obtained; however, ignition timing control needs to be performed at an ignition advance angle which causes an maximum output (referred to as an MBT (Minimum Spark Advance for Best Torque), hereinafter) in accordance with not only the rotation speed of the internal combustion engine and the cylinder intake air flow rate but also other factors such as the temperature of the internal combustion engine, whether or not a knock has occurred, the fuel property, and the EGR ratio, which is the ratio of EGR (Exhaust Gas Recirculation) flow rate to the intake air amount. Among the foregoing factors that provide effects to the MBT, for example, the internal combustion engine temperature and whether or not a knock has occurred can be detected by an internal combustion engine temperature sensor and a knock sensor, respectively; the fuel property, i.e., whether the fuel is regular gasoline or high-octane gasoline can be determined based on whether or not a knock has occurred.
Meanwhile, with regard to the EGR ratio, there are two methods, i.e., a method (referred to as an external EGR, hereinafter) in which an EGR valve is provided in an EGR path that connects the exhaust pipe with the intake pipe and the EGR flow rate is controlled based on the opening degree of the EGR valve and a method (referred to as an internal EGR) in which a variable valve timing mechanism (referred to as a VVT (Variable Valve Timing), hereinafter), which makes the opening/closing timings of an intake valve and an exhaust valve variable, is provided and depending on the opening/closing timings thereof, an overlap period, during which the intake valve and the exhaust valve are concurrently opened, is changed so that the EGR flow rate, which is caused by remaining exhaust gas in the cylinder, is controlled; in some cases, both the methods are concurrently utilized. With regard to the external EGR ratio, the EGR flow rate can approximately be calculated based on the opening degree of the EGR valve, the exhaust gas pressure, and the inner-intake-pipe pressure.
In an internal combustion engine having the foregoing intake/exhaust VVT that can vary the valve opening/closing timings of the intake valve and the exhaust valve, the amount of air that is taken into the cylinder through the intake manifold largely changes depending on the valve timing; therefore, when the effect of the valve timing is not taken into consideration, the accuracy of calculating the amount of air taken into the cylinder may be deteriorated. Furthermore, in recent years, it has become common that control of an internal combustion engine is performed utilizing, as an index, the output torque of the internal combustion engine; even when the output torque is estimated, the thermal efficiency changes in accordance with the cylinder intake air amount and the EGR ratio. Accordingly, in order to calculate the foregoing MBT and furthermore in order to estimate the torque and the thermal efficiency, it is required to accurately calculate the cylinder intake air amount and the EGR ratio.
Thus, Patent Document 1 discloses a technology for accurately calculating a cylinder intake air amount even in an internal combustion engine having such an intake/exhaust VVT. Patent Document 1 discloses a method of calculating a volume efficiency corresponding value, which is an index indicating the amount of air taken into a cylinder through the intake manifold, based on two internal variants, which are referred to as an intake efficiency and an exhaust efficiency, with regard to a method of estimating a cylinder intake air amount, based on the volume efficiency corresponding value and a physical model in which the response delay of the intake system in an interval during which air passes through the throttle valve and enters the cylinder is modeled.